Personal mobility vehicles (PMVs) such as electric wheelchairs are commonplace but nonetheless invaluable technology for people unable to walk independently. While available configurations vary widely, the electrical system of PMVs can be generally divided into three categories: a drive system (electric motors), a drive control unit, and a power source (batteries).
The drive system includes one or more electric motors. Two motors are often used to provide automated steering. Control units and their user interface vary in sophistication according to the needs of the PMV user, but all serve, in some fashion, to control electric power to the driving unit. For example, PMVs for users with sufficient hand control can employ a joystick drive interface, while PMVs for users without hand control may instead employ a head and mouth actuated system. The commercial standard power source for PMVs is two rechargeable, twelve volt batteries connected in series to create DC electric power at twenty-four volts.
The guiding objective for such assistive technology is to provide independence. To that end, recharging systems have been developed that allow wheelchair users to recharge wheelchair batteries without assistance from others. Also to that end, wheelchair users have come to rely on an ever growing number of other assistive devices now available. Common examples include speech synthesizers and remote environmental controllers. Many such devices work with or through computers adapted for attachment to the wheelchair. Furthermore, wheelchair users, no less than others, enjoy the use of consumer electronic devices such as cellular phones and portable radios, tape and CD players.
To be portable with the wheelchair, these accessory devices must also be powered by batteries. Unfortunately, the required battery type and shape varies according to the electronic device. While rechargeable batteries may be available, they must be separately recharged using an appropriate AC driven power supply. For many wheelchair users, this accessory battery recharging or swapping limits their independence because it requires assistance from others.
What is needed is a PMV that can safely and reliably power the electronic accessories as well as the drive system from the same main power source. Accordingly, the present invention provides a PMV having an accessory power source that draws electric power from the main PMV batteries and delivers stable DC electric power at a given accessory voltage.